Anomalous intensity ratios of the resonance to intercombination lines of He-like ions in Nd- and CO2-laser-produced plasmas

Anomalously small values of the intensity ratio alpha of resonance and intercombination lines of He-like ions have been observed in Nd- and CO 2 -laser-produced plasmas. The values of alpha obtained are explained via calculations using a non-stationary ionisation model for the plasma (overheated for CO 2 -laser plasma, and supercooled for expanding Nd-laser plasma). The measurements of the intensity ratio may be used to obtain information on the relative concentrations of H-, He-, and Li-like ions in the plasma. The results obtained allow one to answer the questions: when must the non-stationary character of the plasma ionisation state be taken into account for the observed spectra to be interpreted correctly; and when can one use more simple stationary models for the plasma concerned?.